1. Field of the Invention
The present invention is related to a switching structure embedded in a trigger of a fastening tool, and especially to such a structure capable of controlling switching to contact actuation or full sequential actuation in pursuance of requirement and custom of users, and capable of dust proofing and providing safety in preventing switching by accidentally touching the switching structure.
2. Description of the Prior Art
The fastening tool provided in the present invention is directed specifically to a pneumatic fastening tool. Most of the conventional pneumatic driving tools widely used in the markets each uses a trigger to press a trigger valve which controls a pushing rod in a cylinder driven by compressed air to make strong shot to give fasteners therein for fastening. However, notwithstanding the convenience of using such a pneumatic fastening tool, the fastening tool has a problem of being harmful to people by accidentally touching the trigger. Therefore, most of the fastening tools in the markets are provided with safety devices to limit activating of triggers. And the triggers are distinguished by whether they are provided with safety yokes. Those provided with safety yokes are those each with a safety yoke assembled in the fastener outlet of a fastening tool. A user can only make a triggering after he closely abuts the outlet against a surface of a work piece and presses the safety yoke. Therefore, safety in fastening can be improved. Sequence of such triggers in operation is divided generally into the following two kinds:
The first one is the full sequential trigger, the outlet for shooting shall be closely abutted against a surface of a work piece and the safety yoke can then be pressed for shooting a fastener. Thereafter, both the safety yoke and the trigger have to be returned to the starting position before the tool can be actuated. If the user presses the trigger before pressing the safety yoke, no fastener can be shot. Hence when the user has to change the working area, he must raise the fastening tool and then press the safety yoke again, then the trigger can be activated to shoot a fastener. This is the mode popularly accepted in countries accustomed to the U.S.A system.
The second one is the contact actuation trigger; the trigger can be activated to shoot a fastener whenever the safety yoke and the trigger are both pressed regardless of whether the safety yoke or the trigger is first pressed. Thereby, the user needs only to steadily press the trigger, the safety yoke can be repeatedly pressed, and thus fasteners can be serially shot; or the safety yoke can be steadily pressed, the trigger can be repeatedly pressed to have fasteners shot serially. Hence convenience of operation is increased, this is the mode popularly accepted in European countries.
However, users of fastening tools widely distributed in the world have their customs of use that are very different. Manufacturers are very hard to estimate the yield of production of fastening tools. Therefore, cost of developing, production and storage of fastening tools is very high and makes an extremely large trouble in the art. And the switching structures disclosed in the prior arts all present protrusions on the external surfaces of the fastening tools, conventional mechanisms for contact actuation are more subjected to contamination of dust and dirt, and they are more likely to make hurt of hands when in use; and more, they are more possible to induce wrong switching by accidentally touching the switching structure. Study and development of the present invention aim at solving the above stated undesired problems, and the inventor of the present invention provides the trigger switching structure of a contact actuation or full sequential actuation fastening tools based on his specific experience of years in design, study and development of pneumatic driving tools.